Currently, the widely used computer input devices include keyboard and mouse. Due to the advance of the digital technologies, more and more computer users start to work with digitizer based devices such as digitizers or tablets which allow a user to write and draw upon the surface of a touchpad and have the signals and codes interpreted by a computer. Specifically, the touchpad provides a writing surface for capturing the position and the orientation of an object. In cooperation with the touchpad, a pen-like device is required to create such objects. Most existing pen-like devices, which can be corded or cordless, are not able to generate lines with variable width. To overcome this shortage, pressure sensitive pens are invented. In general, the existing pressure sensitive pens are classified into three categories: 1) capacitive pen, 2) resistive pen, and 3) dual iron-core inductive pen.
No matter which kind of pressure sensitive pen is employed to produce lines with variable width, the basic idea of pressure sensitive techniques is to utilize the variation of the pressure detected. When a resistive pen is used, the pressure variation is difficult to be felt and to be controlled by a user since the working stroke is too short. Consequently, it is difficult to directly present variable thickness of lines using a resistive pen. Capacitive type of pens suffer from similar problems. Dual iron-core inductive pens seem able to overcome the problem and generate lines with variable width. However, the dual iron-core inductive pens have their own drawbacks such as high cost, low production rate.
Based on the findings of the aforementioned drawbacks, it is therefore desirable to introduce an improved method and apparatus to control the pressure variation easily so as to directly present different thickness of lines when a user writes or draws on the surface of a touchpad.